Highly selective n-olefin isomerization process using ZSM-35

ABSTRACT

A process is disclosed for the highly selective skeletal isomerization of linear olefin-containing organic feeds to iso-olefins at high levels of feed conversion wherein linear olefins, e.g., n-butenes, are contacted with catalyst comprising ZSM-35 under skeletal isomerization conditions which can include temperatures of 100 to 750° C. The process uses a catalyst composition comprising ZSM-35, e.g., microcrystalline ZSM-35 having a crystal size whose largest dimension is no greater than 0.5 micron and whose ratio of its second largest dimension to said largest dimension ranges from 0.5 to 1. The process exhibits enhanced catalyst cycle life where the ZSM-35 is composited with a silica-containing matrix to provide a catalyst composite having a total pore volume greater than 0.6 cc/g or 300 +  angstroms pore volume of greater than 0.1 cc/g.

REFERENCE TO COPENDING APPLICATION

This is a continuation of application Ser. No. 07/962,637, filed on Oct.16, 1992, now abandoned, which is a continuation-in-part of U.S. patentapplication Ser. No. 07/760,287, now abandoned, filed Sep. 16, 1991, theentire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to a method for the high level conversion ofn-olefin-containing, e.g., n-butene-containing, hydrocarbon streams toiso-olefin-rich, e.g., isobutene-rich product streams under skeletalisomerization conditions which include temperatures of 100° to 750° C.The method uses a catalyst composition comprising ZSM-35, e.g.,microcrystalline ZSM-35 having a crystal size whose largest dimension isno greater than 0.5 micron and whose ratio of its second largestdimension to said largest dimension ranges from 0.5 to 1. Enhancedcatalyst cycle life is obtained when the ZSM-35 is composited with asilica-containing matrix which results in a large pore catalystcomposite having a total pore volume of at least 0.6 cc/g or 300+angstroms pore volume of at least 0.1 cc/g.

BACKGROUND OF THE INVENTION

The demand for iso-alkenes has recently increased. For example,relatively large amounts of isobutene are required for reaction withmethanol or ethanol over an acidic catalyst to produce methyl tert-butylether (MTBE) or ethyl tert-butyl ether (ETBE) which is useful as anoctane enhancer for unleaded gasolines. Isoamylenes are required forreaction with methanol over an acidic catalyst to produce tert-amylmethyl ether (TAME). With passage of the Clean Air Act in the UnitedStates mandating increased gasoline oxygenate content, MTBE, ETBE andTAME have taken on new value as clean-air additives, even for loweroctane gasolines. Lead phasedown of gasolines in Western Europe hasfurther increased the demand for such oxygenates.

An article by J. D. Chase, et al., Oil and Gas Journal, Apr. 9, 1979,discusses the advantages one can achieve by using such materials toenhance gasoline octane. The blending octane values of MTBE when addedto a typical unleaded gasoline base fuel are RON=118, MON=101,R+M/2=109. The blending octane values of TAME when added to a typicalunleaded gasoline base fuel are RON=112, MON=99, R+M/2=106. Isobutene(or isobutylene) is in particularly high demand as it is reacted withmethanol to produce MTBE.

The addition of shape-selective zeolite additives such as ZSM-5 tocracking catalysts, e.g., those used in fluidized catalytic cracking(FCC), is beneficial in producing gasoline boiling range product ofincreased octane rating. However, increased amounts of olefins result,including n-butenes, creating a need for their conversion to highervalue products such as isobutene which can be used to produce MTBE.

Butene exists in four isomers: butene-1, cis-butene-2, its stereo-isomertrans-butene-2, and isobutene. Conversions between the butenes-2 isknown as geometric isomerization, whereas that between butene-1 and thebutenes-2 is known as position isomerization, double-bond migration, orhydrogen-shift isomerization. The aforementioned three isomers are notbranched and are known collectively as normal or n-butenes. Conversionof the n-butenes to isobutene, which is a branched isomer, is widelyknown as skeletal isomerization.

The reaction of tertiary olefins with alkanol to produce alkyl tertiaryalkyl ether is selective with respect to iso-olefins. Linear olefins areunreactive in the acid catalyzed reaction, even to the extent that it isknown that the process can be utilized as a method to separate linearand iso-olefins. The typical feedstream of FCC C₄ or C₄ + crackate usedto produce tertiary alkyl ethers in the prior art which contains normalbutene and isobutene utilizes only the branched olefin inetherification. This situation presents an exigent challenge to workersin the field to discover a technically and economically practical meansto utilize linear olefins, particularly normal butene, in themanufacture of tertiary alkyl ethers.

In recent years, a major development within the petroleum industry hasbeen the discovery of the special catalytic capabilities of a family ofzeolite catalysts based upon medium pore size shape selectivemetallosilicates. Discoveries have been made leading to a series ofanalogous processes drawn from the catalytic capability of zeolites inthe restructuring of olefins.

European Patent 0026041 to Garwood, incorporated herein by reference,discloses a process for the restructuring of olefins in contact withzeolite catalyst to produce iso-olefins, followed by the conversion ofiso-olefins to MTBE and TAME. The restructuring conditions comprisetemperature between 204° C. and 315° C. and pressure below-51 kPa.

In European Patent 0247802 to Barri et al., it is taught that linearolefins can be restructured in contact with zeolite catalyst, includingTheta-1 (ZSM-22) and ZSM-23, to produce branched olefins. Therestructuring conditions comprise temperature between 200°-550° C.,pressure between 100 and 5000 kPa and WHSV between 1 and 100.Selectivities to isobutene up to 91.2% are reported using a calcinedTheta-1 tectometallosilicate at 400° C. and 30.6% 1-butene conversion.

U.S. Pat. No. 3,992,466 to Plank et al. teaches the use of ZSM-35 as acatalyst for hydrocarbon conversion reactions, including "isomerizationof aromatics, paraffins and olefins."

U.S. Pat. No. 4,922,048 to Harandi discloses the use of a wide varietyof medium pore size zeolites, e.g., ZSM-5, ZSM-11, ZSM-12, ZSM-22,ZSM-23, ZSM-35 and ZSM-48, in low temperature (232°-385° C.) olefininterconversion of C₂ -C₆ olefins to products including tertiary C₄ -C₅olefins and olefinic gasoline.

U.S. Pat. No. 4,886,925 to Harandi discloses low pressure hightemperature conversion of light olefins to produce higher olefins richin isoalkenes. The process converts C₂₊ n-alkenes to a productcomprising C₄ -C₆ alkenes rich in iso-alkenes, C₇₊ olefinic gasolineboiling range hydrocarbons, and unconverted hydrocarbons over ZSM-5. Thereference teaches further treatment of the alkene effluent with methanolin the presence of medium pore size zeolites such as ZSM-5, ZSM-11,ZSM-12, ZSM-35, ZSM-38 and ZSM-48.

U.S. Pat. No. 4,996,386 to Hamilton, Jr. discloses concurrentisomerization and disproportionation of hydrocarbon olefins using aferrierite/Mo/W/Al₂ O₃ catalyst. The catalyst exemplified produces fewerbranched olefins than a comparable material free of ferrierite and thereference teaches that ferrierite-containing catalysts exhibit improvedselectivity to linear olefins than conventionally prepareddisproportionation catalysts.

All of the above references are incorporated herein by reference.

Despite the efforts exemplified in the above references, the skeletalisomerization of olefins e.g., to produce isobutene, has been hamperedby relatively low conversion and/or selectivity to isobutene perhapsowing to the lability of these olefins. It is further known thatskeletal isomerization becomes more difficult as hydrocarbons of lowermolecular weight are used, requiring more severe operating conditions,e.g., higher temperatures and lower linear olefin partial pressures.

Generally, the conversion of n-butenes to iso-butene is conducted atselectivities below 90%. In order to obtain higher selectivities,operation at high temperatures (>500° C.) and with high feed dilution(butene partial pressure, typically less than 5 psia (34.5 kPa)) isgenerally required. Selectivities of greater than 85%, 90%, 95% or even99% are highly advantageous in commercial conversion of n-butenes toisobutene in order to avoid the need to separate out materials otherthan n-butene from the product stream. Such high selectivities willpermit direct (cascading) or indirect introduction of the isomerizereffluent to an etherification zone where isobutene is reacted withalkanol to produce alkyl tert-butyl ether, e.g., MTBE. Unconvertedn-butenes in the isomerizer effluent can be withdrawn either before theetherification zone or preferably, from the etherification zone effluentinsofar as the etherification reaction utilizes only the isobutenecomponent of the isomerizer stream. Unreacted n-butenes from theetherification zone effluent can be recycled to the isomerizer wherethey are converted to isobutene at high selectivity. If the recyclestream contains not only unconverted linear olefins, e.g., n-butenes,but also by-products such as other olefins (e.g., propylene) orparaffins, they have to be removed from the recycle stream, such as bydistillation or by taking a slip stream. These removal steps areexpensive and can lead to considerable loss of not only the by-productsbut butenes as well. These losses are larger when the by-products formedare present in higher concentration. Thus, even small improvements inthe isobutene selectivity during n-butene isomerization have a majoreffect on the commercial viability of the process. However, highselectivities in skeletal isomerization processes have generallyrequired low linear olefin partial pressures and high temperatures whichplace substantial limitations on such processes. It would, therefore, beadvantageous to provide a skeletal isomerization catalyst capable ofmaintaining relatively high selectivity at low temperatures and highlinear olefin partial pressures.

Further enhancement of total yield of iso-olefin can be effected byenhancing overall conversion of the n-olefin-containing feedstream. Withthis object in mind, it would be advantageous to provide a skeletalisomerization catalyst capable of maintaining a high level of conversionas well as high iso-olefin selectivity, even at relatively lowtemperatures, e.g., no greater than 450° C. and high n-olefin spacevelocities, e.g., no less than 5, e.g., no less than 70.

SUMMARY OF THE INVENTION

The present invention provides a method for conversion of linear olefinsto corresponding iso-olefins of the same carbon number which comprisescontacting a linear olefin-containing organic feedstock with a catalystcomprising ZSM-35, preferably microcrystalline ZSM-35, under skeletalisomerization conditions, including temperatures between about 100 and750° C. Microcrystalline ZSM-35 can be described as having a crystalmorphology whose largest dimension is no greater than 0.5 micron, andwhose ratio of its second largest dimension to said largest dimensionranges from about 0.5 to 1. In one aspect, the present inventionprovides a method of enhanced cycle life where the ZSM-35 is compositedwith a silica-containing matrix under conditions which provide acomposite having a total pore volume of at least 0.6 cc/g or 300+angstroms pore volume of at least 0.1 cc/g.

The high selectivity of ZSM-35 in the present invention results in largepart from isomerization occurring without significant conversion tolighter and heavier molecules. This phenomenon, it is believed, is aconsequence of the pore structure of ZSM-35 which promotes isomerizationat a much faster rate than the reaction by which say, butene, isconverted to lighter (mostly propylene) and heavier olefins (olefininterconversion reaction). Moreover, such isomerization takes placewithout significant cracking of the feed or hydrogenation ordehydrogenation effects resulting in the formation of, say, n-butane orbutadiene. The present invention can be used to effect conversion oflinear olefins to iso-olefins while resulting in less than 30%, 10%, 5%or even less than 1% by weight of converted product having lower orhigher average carbon number.

In one aspect, the present invention can provide enhanced overall yieldsof iso-olefin product from linear olefin-containing feeds by a highlyselective conversion of linear olefins to corresponding iso-olefins ofthe same carbon number, e.g., n-butenes to isobutene, at enhanced linearolefin conversion levels.

The present invention's utilization of microcrystalline ZSM-35 resultsin not only a highly selective conversion of n-olefins to iso-olefins,but a conversion of n-olefin feed at significantly higher levels, over abroad temperature range, particularly at temperatures of less than about500° C., 450° C. or even 400° C.

DESCRIPTION OF THE FIGURES

FIG. 1 depicts the respective conversions and products obtained forZSM-22, ZSM-23 and ZSM-35 in skeletal isomerization of 1-butene at 550°C.

FIG. 2 depicts the respective conversions and products obtained forZSM-22, ZSM-23 and ZSM-35 in skeletal isomerization of 1-butene at 400°C.

FIG. 3 is a selectivity/conversion plot comparing the performance ofZSM-23 and ZSM-35.

FIG. 4 depicts the conversions and products obtained for ZSM-35 inskeletal isomerization of 1-butene at high WHSV, low temperatures andhigh butene partial pressures.

FIG. 5 is a transmission electron microscopy (TEM) micrograph of amicrocrystalline ZSM-35 sample prepared in accordance with the procedureset out in Example 1.

FIG. 6 is a transmission electron microscopy (TEM) micrograph of largecrystal ZSM-35 of Example 12.

FIG. 7 is a transmission electron microscopy (TEM) micrograph of largecrystal synthetic ferrierite of Example 13.

FIG. 8 depicts 1-butene conversion and iso-butene selectivity overtemperature at 165 WHSV from Example 14.

FIG. 9 depicts 1-butene conversion and iso-butene selectivity overtemperature at 2 WHSV from Example 15.

FIG. 10 depicts the low aging rate of microcrystalline ZSM-35 comparedto large crystal synthetic ferrierite where n-butene conversion isplotted as a function of cumulative 1-butene throughput.

FIG. 11 compares the aging rates of alumina-bound ZSM-35 catalyst fromExample 16 and silica-bound ZSM-35 catalyst of enhanced pore volume fromExample 17.

FIG. 12 compares selectivity versus conversion in n-butene conversionfor the alumina-bound catalyst of Example 16 and the silica-boundcatalyst of enhanced pore volume from Example 17.

FIG. 13 compares the effects of binder pore size on ZSM-35 aging inbutene skeletal isomerization for the small pore silica-bound catalystof Example 4, versus the large-pore silica-bound catalyst of Example 17.

FIG. 14 compares selectivity versus conversion for the small poresilica-bound catalyst of Example 4, compared with the large-poresilica-bound catalyst of Example 17.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a process which converts a linearolefin-containing hydrocarbon feedstream to an iso-olefin rich productat high levels of conversion and high iso-olefin selectivity over acatalyst comprising material having the structure of ZSM-35 andpreferably having a crystal size whose largest dimension is no greaterthan 0.5 micron, preferably no greater than 0.25 micron, more preferablyno greater than 0.15 micron, e.g., no greater than 0.1 micron, underskeletal isomerization conditions.

The skeletal isomerization reaction of the present invention is carriedout at temperatures between 100 and 750° C.; weight hourly spacevelocity based on linear olefin in the feed between 0.1 and 500 WHSV;and linear olefin partial pressure between 2 and 2000 kPa. The preferredconditions are temperatures between 150 and 600° C., more preferablybetween 200 and 550° C., WHSV between 0.5 and 400, more preferablybetween 1 and 100; and a linear olefin partial pressure between 10 and500 kPa, more preferably between 20 and 200 kPa. Under these conditionsthe conversion of linear olefin, e.g., n-butene, can be at least 20%,preferably at least 35% and more preferably at least 45%. Theselectivity to iso-olefin, e.g., isobutene, is at least 75%, preferablyat least 85%, 90%, or even 95%.

The present invention is especially suited to processes carried out athigh linear olefin to iso-olefin selectivity, e.g, at least 60% atrelatively low conversion temperatures and high linear olefin partialpressures. Such processes can maintain selectivities of at least 75, 85or 95% at a conversion temperature less than or equal to: 550, 450, 400or even 350° C., and linear olefin partial pressures above 2 psia (14kPa), e.g., above 5 psia (34 kPa). Such processes can be carried out atan overall conversion of linear olefins of at least 30, 35, 40, or 45 wt% or higher. The present method is particularly effective when operatingat lower temperatures, e.g., less than 450° C. and at relatively highWHSV, e.g., no less than 1, 5, or even 20. Under these conditions isobserved a significant improvement in catalytic activity as evidenced byenhanced conversion of linear olefins when compared with methodsutilizing large crystal ZSM-35 materials.

Preferred feedstreams for use in the present invention include C₄ orC₄ + hydrocarbon feedstreams. Linear olefins suited to use in thepresent invention may be derived from a fresh feedstream, preferablycomprising n-butenes and/or n-pentenes, or from the effluent of aniso-olefin etherification reactor which employs alkanol and C₄ or C₄ +hydrocarbon feedstock. Typical hydrocarbon feedstock materials forisomerization reactions according to the present invention includeolefinic streams, such as cracking process light gas containing buteneisomers in mixture with substantial amounts of paraffins includingn-butane and isobutane. The C₄ components usually contain a major amountof unsaturated compounds, such as 10-40% isobutene, 20-55% linearbutenes, and small amounts of butadiene. Also, C₄ + heavier olefinichydrocarbon streams may be used, e.g C₄ to C_(10') preferably C₄ to C₆olefinic hydrocarbon streams, e.g., light FCC gasoline. Feedstockscomprising at least 5 wt % n-butenes or n-pentenes can be used in thepresent method.

ZSM-35 is more particularly described in U.S. Pat. No. 4,016,245, theentire contents of which are incorporated herein by reference.

For present purposes, "ZSM-35" is considered equivalent to its isotypes,which include ferrierite (P. A. Vaughan, Acta Cryst. 21, 983 (1966));FU-9 (D. Seddon and T. V. Whittam, European Patent B-55,529, 1985);ISI-6 (N. Morimoto, K. Takatsu and M. Sugimoto, U.S. Pat. No. 4,578,259,1986); monoclinic ferrierite (R. Gramlich-Meier, V. Gramlich and W. M.Meier, Am. Mineral. 70, 619 (1985)); NU-23 (T. V. Whittam, EuropeanPatent A-103,981, 1984); and Sr-D (R. M. Barrer and D. J. Marshall, J.Chem. Soc. 1964, 2296 (1964)). Preferably the catalyst comprises ZSM-35in its hydrogen-exchanged form, HZSM-35.

An example of a piperidine-derived ferrierite is more particularlydescribed in U.S. Pat. No. 4,343,692, the entire contents of which areincorporated herein by reference other synthetic ferrierite preparationsare described in U.S. Pat. Nos. 3,933,974; 3,966,883; 4,000,248;4,017,590; and 4,251,499, the entire contents of all being incorporatedherein by reference. Further descriptions of ferrierite are found inBibby et al, "Composition and Catalytic Properties of SyntheticFerrierite," Journal of Catalysis, 35, pages 256-272 (1974).

As noted above, microcrystalline ZSM-35 has a morphology whose largestdimension is no greater than 0.5 micron, preferably no greater than 0.25micron or even 0.1. Even more preferably such crystals can be describedas falling within the range of 0.03 to 0.08 micron by 0.03 to 0.08micron by ≦0.05 micron.

Microcrystalline ZSM-35 is made by control of the synthesis formulationand synthesis temperature, with lower temperature favoring smallercrystals.

The zeolite catalyst used is preferably at least partly in the hydrogenform, e.g., HZSM-35, but other cations, e.g., rare earth cations, mayalso be present. When the zeolites are prepared in the presence oforganic cations, they may be quite inactive possibly because theintracrystalline free space is occupied by the organic cations from theforming solution. The zeolite may be activated by heating in an inertatmosphere to remove the organic cations e.g., by heating at over 500°C. for 1 hour or more. The hydrogen form can then be obtained by baseexchange with ammonium salts followed by calcination e.g., at 500° C. inair. Other cations, e.g., metal cations, can be introduced byconventional base exchange or impregnation techniques.

The ZSM-35 may be incorporated in another material usually referred toas a matrix or binder. Such matrix materials include synthetic ornaturally occurring substances as well as inorganic materials such asclay, silica and/or metal oxides. The latter may be either naturallyoccurring or in the form of gelatinous precipitates or gels includingmixtures of silica and metal oxides. Naturally occurring clays which canbe composited with the zeolite include those of the montmorillonite andkaolin families, which families include the subbentonites and thekaolins commonly known as Dixie, McNamee, Georgia and Florida clays orothers in which the main mineral constituent is halloysite, kaolinite,dickite, nacrite or anauxite. Such clays can be used in the raw state asoriginally mined or initially subjected to calcination, acid treatmentor chemical modification.

In addition to the foregoing materials, the zeolites employed herein maybe composited with a porous matrix material, such as silica, alumina,zirconia, titania, silica-alumina, silica-magnesia, silica-zirconia,silica-thoria, silica-beryllia, silica-titania as well as ternarycompositions such as silica-alumina-thoria, silica-alumina-zirconia,silica-alumina-magnesia and silica-magnesia-zirconia. The matrix can bein the form of a cogel. A mixture of these components could also beused.

Of all the foregoing materials, silica may be preferred as the matrixmaterial owing to its relative inertness for catalytic crackingreactions which are preferably minimized in the instant isomerizationprocesses. Alternatively, silica-containing matrix containing a minoramount of aluminum may be employed. The relative proportions of finelydivided ZSM-35 and inorganic oxide gel matrix vary widely with thezeolite content ranging from about 1 to about 90 percent by weight andmore usually in the range of about 30 to about 80 percent by weight ofthe composite.

It is believed that using a silica binder and controlling extrusionconditions by means such as moisture control to ensure increased porevolume results in a catalyst which ages more slowly under skeletalisomerization conditions, resulting in increased cycle length. Suchconditions increase total pore volume to greater than 0.6 g/cc, or 300⁺angstroms pore volume to greater than 0.1 cc/g. These increased porevolumes can be obtained by increasing moisture content of the extrudate.The resulting catalyst composite is of particular utility insofar as itsuse can result in increased cycle length without any significant loss ofiso-olefin selectivity.

The regeneration of spent zeolite catalyst used in the isomerizationreaction is carried out oxidatively or hydrogenatively employingprocedures known in the art. The catalyst of the present invention canbe readily reactivated without significantly reducing selectivity forisobutene by exposing it to hydrogen for a suitable period, e.g.,overnight.

In order to obtain desired linear olefin skeletal isomerizationactivity/selectivity, ZSM-35, preferably in the hydrogen form, shouldhave an alpha value of at least 5, preferably at least 50 when used inthe catalyst of the present invention. Alpha value, or alpha number, ofa zeolite is a measure of zeolite acidic functionality and is more fullydescribed together with details of its measurement in U.S. Pat. No.4,016,218, J. Catalysis, 6, pp. 278-287 (1966) and J. Catalysis, 61, pp.390-396 (1980). The experimental conditions cited in the latterreference are used for characterizing the catalysts described herein.

The examples which follow illustrate the invention without restrictingit in any way.

EXAMPLE 1

Preparation of MicroCrystalline ZSM-35

1.18 parts of aluminum sulfate (17.2% Al₂ O₃) were added to a isolutioncontaining 9.42 parts H₂ O and 1.38 parts of 50% NaOH solution in anautoclave. 0.03 parts of ZSM-35 seeds and 3.20 parts of Hi-Silprecipitated silica were added with agitation, followed by 1.0 part ofpyrrolidine.

The reaction mixture had the following composition, in mole ratios:

    ______________________________________                                                SiO.sub.2 /Al.sub.2 O.sub.3                                                           21.5                                                                  OH.sup.- /SiO.sub.2                                                                   0.11                                                                  H.sub.2 O/Al.sub.2 O.sub.3                                                            13.5                                                                  R/Al.sub.2 O.sub.3                                                                    6.45                                                          ______________________________________                                    

where R=pyrrolidine. The mixture was crystallized at 105° C. for 74hours with stirring. The ZSM-35 product was filtered, washed withdeionized water, and dried at 120° C.

The chemical composition of the product was, in weight percent:

    ______________________________________                                               SiO.sub.2 76.7                                                                Al.sub.2 O.sub.3                                                                        6.4                                                                 Na        0.84                                                                C         7.26                                                                N         2.03                                                                Ash @ 1000° C.                                                                   85.5                                                         ______________________________________                                    

with a silica/alumina ratio for the product, in moles, of 20.3/1.

Scanning electron microscopy and transmission electron microscopyindicate the ZSM-35 crystals have platelet morphology with a broaddistribution of crystal sizes having the largest dimension of up to 0.05to 0.1 micron. FIG. 5 is a TEM micrograph of the ZSM-35 thus prepared.

EXAMPLE 2

Preparation of HZSM-35/SiO₂ Mix

The as-synthesized ZSM-35 of Example 1 was calcined in nitrogen for 3hours at 538° C., then exchanged two times at room temperature with 1NNH₄ NO₃ solution to convert it to the ammonium form, dried at 120° C.,and calcined in air for 6 hours at 538° C. to convert it to the hydrogenform. The zeolite was dry mixed with a precipitated silica, inproportion to give 65% ZSM-35/35% silica after calcination, formed intopellets, and calcined in air for 3 hours at 538° C.

EXAMPLE 3

Preparation of Silica-Bound HZSM-35

A catalyst was prepared by dry mixing the as-synthesized ZSM-35 ofExample 1 with precipitated silica, in proportion to give, aftercalcination, 65% ZSM-35/35% silica in the catalyst. A solutioncontaining 2% NaOH (based on solids) was added to the mix to create anextrudable mull, the mix was extruded to 1/16 inch (1.6 mm) diameter anddried at 120° C. The extrudate was exchanged two times with 1N NH₄ NO₃solution at room temperature, rinsed with deionized water, dried at 120°C. and calcined in nitrogen for 3 hours at 538° C. It was againexchanged with 1N NH₄ NO₃ solution two times at room temperature, driedat 120° C., and calcined in air for 9 hours at 538° C.

EXAMPLE 4

Preparation of Silica-Bound HZSM-35

A catalyst was prepared by dry mixing the as-synthesized ZSM-35 ofExample 1 with precipitated silica. Colloidal silica, in proportion togive 65% ZSM-35/35% silica after calcination, and water were added tothe dry mix to obtain an extrudable mull. The mull was extruded to 1/16inch (1.6 mm) diameter, dried at 120° C., calcined in nitrogen for threehours at 538° C., and then in air for 6 hours at 538° C. The extrudatewas exchanged two times with 1N NH₄ NO₃ solution at room temperature,dried at 120° C. and calcined in air for 3 hours at 538° C. The totalpore volume of this catalyst was 0.55 cc/g and 300⁺ angstrom pore volumewas measured as 0.04 cc/g.

EXAMPLE 5

Isomerization of 1-Butene with ZSM-22, ZSM-23 and ZSM-35 at 550° C.

ZSM-22 was prepared by charging 48.2 parts water to an autoclavefollowed by 5.0 parts KOH solution (45% by weight), 1.0 part aluminumsulfate (17.2% Al₂ O₃) and 0.45 parts seeds. After mixing thoroughly,8.2 parts of Ultrasil VN3 precipitated silica (Degussa), then 3.6 partsof ethylpyridinium bromide (50% by weight) were added and mixedthoroughly. After aging the reaction mixture for 16 hours at 93° C.while stirring, the temperature was increased to 160° C. and maintaineduntil crystallization was complete. The product was identified as ZSM-22by X-ray diffraction. The slurry was filtered, washed and dried. Aportion of the zeolite was calcined in flowing nitrogen for 3 hours at538° C. and 3 hours in air at the same temperature. The cooled zeolitewas exchanged with 1N NH₄ NO₃ (5 cc/g zeolite) at room temperature forone hour then washed with water. The exchange procedure was repeated andthe catalyst dried at 120° C. The zeolite was then calcined in flowingair for 3 hours at 538° C., then blended 65 parts zeolite and 35 partsUltrasil VN3 and pelleted. The pellets were sized 14/24 mesh andrecalcined at 538° C. in flowing air for 3 hours.

ZSM-23 was prepared by charging 85.5 parts water to an autoclavefollowed by 2.64 parts KOH solution (45% by weight), 1.0 part aluminumsulfate (17.2% Al₂ O₃) and 0.5 parts ZSM-23 seeds (100% basis). Aftermixing thoroughly, 14.5 parts of Ultrasil VN3 precipitated silica(Degussa), then 5.1 parts of pyrrolidine were added and mixedthoroughly. The autoclave was heated to 160° C. with stirring andmaintained at these conditions until crystallization was complete Theproduct was identified as ZSM-23 by X-ray diffraction. After flashingthe pyrrolidine, the slurry was cooled, washed, filtered and dried.Eight parts of the dried ZSM-23 were combined with 1 part Ultrasil VN3and 1 part Ludox colloidal silica (DuPont), mulled and extruded to form1/16 inch pellets which were dried at 120° C. The pellets were thencalcined in flowing nitrogen for 2 hours at 538° C. and 3 hours in airat the same temperature. The cooled catalyst was exchanged with 1N NH₄NO₃ (5 cc/g catalyst) at room temperature for one hour then washed withwater. The exchange procedure was repeated and the catalyst dried at120° C. The exchanged extrudate was then calcined at 538° C. in flowingair for 3 hours.

The above-prepared ZSM-22 and ZSM-23, and ZSM-35 prepared in accordancewith Example 3 above were used in butene skeletal isomerizationreactions. The approximate experimental conditions were:

    ______________________________________                                        Temperature           550° C.                                          Pressure              177 kPa                                                 1-Butene WHSV         65 hr.sup.-1                                            N.sub.2 /Butene in feed                                                                             3 vol/vol                                               ______________________________________                                    

FIG. 1 graphically depicts the respective conversions and productsobtained for ZSM-22, ZSM-23 and ZSM-35. Under these conditionsselectivities of 83.5%, 88.2% and 95%, respectively, were obtained.

EXAMPLE 6

Isomerization of 1-Butene with ZSM-22, ZSM-23 and ZSM-35 at 400° C.

ZSM-22 and ZSM-23 prepared in accordance with Example 5, and ZSM-35prepared in accordance with Example 3 above were used in butene skeletalisomerization reactions. The approximate experimental conditions were:

    ______________________________________                                        Temperature           400° C.                                          Pressure              177 kPa                                                 1-Butene WHSV         65 hr.sup.-1                                            N.sub.2 /Butene in feed                                                                             3 vol/vol                                               ______________________________________                                    

FIG. 2 graphically depicts the respective conversions and productsobtained for ZSM-22, ZSM-23 and ZSM-35. Under these conditionsselectivities of 54.3%, 51.1% and 93.2%, respectively, were obtained.ZSM-35 maintains selectivity above 90% even at temperatures whichsignificantly reduce selectivities for ZSM-22 and ZSM-23.

EXAMPLE 7

Isomerization of Butene With ZSM-23 and ZSM-35 at 400° C.

ZSM-22 and ZSM-23 prepared in accordance with Example 5, and ZSM-35prepared in accordance with Example 3 above were used in 1-buteneskeletal isomerization reactions at 400° C. and varying n-buteneconversions over a wide range of process conditions. FIG. 3 is aselectivity/conversion plot comparing the performance of the twocatalysts. At 30 to 40% conversion, selectivity of ZSM-23 ranges between30 and 80%. In contrast, selectivity of ZSM-35 ranges from 90 to 99%.Indeed, selectivity of ZSM-35 remains relatively flat at greater than85% all the way from about 2 to 40% conversion.

EXAMPLE 8

Isomerization of 1-Butene with HZSM-35/SiO₂ Mix

The ZSM-35-containing catalyst of Example 2 was used to process a1-butene feed under four sets of skeletal isomerization conditionscomprising two temperatures and two relatively low 1-butene partialpressures. The conditions and compositions of the product streams fromRuns 1 to 4 are set out in Table 1 below. Selectivity for isobuteneranged from 93.2 to 99%.

                  TABLE 1                                                         ______________________________________                                        Butene Skeletal Isomerization Using ZSM-35/SiO.sub.2 Mix                      Catalyst: ZSM-35/Silica Mixed (65/35), Silica/Alumina = 20,                   Catalyst Alpha = 96                                                           Run Number:      1      2        3    4                                       ______________________________________                                        Feed: 1-Butene/Nitrogen                                                       Feed 1-Butene WHSV:                                                                            76     75       21   21                                      Feed Nitrogen/1-Butene                                                                         3      3        10   10                                      (vol/vol)                                                                     Temperature (°C.)                                                                       400    550      400  550                                     Pressure (kPa    163    170      156  163                                     Hours On Stream  2      6        9    14.5                                    Composition of the Product Stream (%)                                         Normal Butenes   61.9   62.9     66.8 62.2                                    Isobutene        35.5   35.2     32.9 36.2                                    Propene          1.1    0.6      0.2  0.4                                     Pentenes         0.8    0.3      0    0                                       Other C.sub.5-   0.7    0.9      0.1  1.2                                     C.sub.6+         0      0.1      0    0                                       n-Butene Conversion (%)                                                                        38.1   37.1     33.2 37.8                                    Isobutene Selectivity (%)                                                                      93.2   95       99   95.6                                    ______________________________________                                    

EXAMPLE 9

Isomerization of 1-Butene with Silica-Bound ZSM-35

The ZSM-35-containing catalyst of Example 3 was used to process a1-butene feed under four sets of skeletal isomerization conditionscomprising two temperatures and two relatively low 1-butene partialpressures. The conditions and compositions of the product streams fromRuns 1 to 4 are set out in Table 2 below. A comparison of Tables 1 and 2shows that silica binding has no significant deleterious effect onperformance between silica-bound ZSM-35 and ZSM-35/SiO₂ mix catalysts.

                  TABLE 2                                                         ______________________________________                                        Butene Skeletal Isomerization Using Silica-Bound ZSM-35                       Run Number:      1      2        3    4                                       ______________________________________                                        Feed: 1-Butene/Nitrogen                                                       Feed 1-Butene WHSV:                                                                            65.9   65.5     18.4 18.5                                    Feed Nitrogen/1-Butene                                                                         3      3        10   10                                      (vol/vol)                                                                     Temperature (°C.)                                                                       400    550      400  550                                     Pressure (kPa)   161    171      158  165                                     Hours On Stream  2.5    6.5      9.5  14.5                                    Composition of the Product Stream (%)                                         Normal Butenes   65     63.3     64.5 63                                      Isobutene        32.8   34.8     35.1 36.0                                    Propene          0.84   0.6      0.2  0.48                                    Pentenes         0.65   0.25     0    0                                       Other C.sub.5-   0.62   0.94     0.2  0.55                                    C.sub.6+         0.1    0.13     0    0                                       n-Butene Conversion (%)                                                                        35     36.7     35.5 37                                      Isobutene Selectivity (%)                                                                      93.7   95       98.9 97.2                                    ______________________________________                                    

EXAMPLE 10

1-Butene Conversion at Low Temperature, High Pressure Conditions

1-Butene was converted over the HZSM-35 catalyst of Example 4 under thefollowing conditions:

    ______________________________________                                        Temperature           400° C.                                          Pressure              200 kPa                                                 1-Butene WHSV         20 to 65                                                Total WHSV            40 to 130                                               N.sub.2 /Butene       1 (vol/vol)                                             ______________________________________                                    

The results of this conversion are depicted in FIG. 4 and show thatZSM-35, unlike ZSM-22 and ZSM-23, performs well, particularly respectingselectivity, even at high WHSV, low temperatures and high butene partialpressures.

EXAMPLE 11

1-Pentene Conversion over ZSM-35

1-Pentene was converted over the ZSM-35/SiO₂ catalyst of Example 3 underthe following conditions:

    ______________________________________                                        Temperature           400° C.                                          Pressure              200 kPa                                                 1-Pentene WHSV        123 hr.sup.-1                                           Hours On Stream       10.                                                     ______________________________________                                    

This conversion yielded the following product distribution (wt %):

    ______________________________________                                        Total C4-           1.7                                                       2-methyl-1-butene   19.4                                                      2-methyl-2-butene   51.5                                                      3-methyl-1-butene   0.1                                                       1-pentene           2.2                                                       trans-2-pentene     14.9                                                      cis-2-pentene       9.6                                                       Total C6+           0.7                                                       IC5═/NC5═ in product                                                                      2.66.                                                     ______________________________________                                    

The above results indicate that linear pentene is converted to branchedpentenes (to near equilibrium) over ZSM-35 with excellent selectivity.

EXAMPLE 12

Preparation of Large Crystal ZSM-35

0.14 parts of aluminum sulfate (17.2% Al₂ O₃) were added to a solutioncontaining 6.5 parts water and 0.43 parts of 50% NaOH solution in athird autoclave. 0.74 parts of PPG Hi-Sil 233™ precipitated silica wereadded with 1.0 part of pyrrolidine. The mixture was crystallized at 175°C. for twenty four hours with stirring. The zeolite was recovered byfiltration and washing, then calcined with nitrogen at 540° C. todecompose the organic, exchanged with 1N NH₄ NO₃ solution to removesodium and finally calcined in air to remove residual organic. Scanningelectron microscopy and transmission electron microscopy indicate theZSM-35 crystals have platelet morphology with a broad distribution ofcrystal sizes having the largest dimension of up to 1 to 2 microns. FIG.6 is a TEM micrograph of the large crystal ZSM-35 thus prepared.

EXAMPLE 13

Large Crystal Synthetic Ferrierite

A synthetic ferrierite obtained from Tosoh had a silica to alumina molarratio of 16.8/1, an alpha value of 81, and a surface area of 219 m^(2/)g. Scanning electron microscopy and transmission electron microscopyindicate the synthetic ferrierite crystals have platelet morphology witha broad distribution of crystal sizes having the largest dimension of upto 1 to 2 microns. FIG. 7 is a TEM micrograph of the large crystalsynthetic ferrierite thus prepared.

The synthetic ferrierite was dry mixed with precipitated silica in aratio to achieve 65% ferrierite/35% silica after processing. Water andsodium hydroxide (2 parts NaOH/35 parts silica) was added to obtain anextrudable mixture. The mix was extruded to 1/16 inch (1.6 mm) diameterpellets and dried at 100° C. The dried extrudate was treated twice with1N NH₄ NO₃ for 1 hour at room temperature and washed with water. Afterdrying at 100° C., the extrudate was calcined in nitrogen at 538° C. for3 hours. Following cooling, the calcined material was exchanged twicewith 1N NH₄ NO₃ for 1 hour and dried. The catalyst was then calcined for6 hours at 538° C. in air.

EXAMPLE 14

Isomerization of 1-Butene with Microcrystalline ZSM-35 and Large CrystalZSM-35

The microcrystalline ZSM-35 of Example 4 and the large crystal ZSM-35 ofExample 12 were used in 1-butene skeletal isomerization reactionscarried out at 300, 400, 500 and 550° C., and at 165 WHSV, 30 psia.1-Butene conversion and iso-butene selectivity over temperature aredepicted in FIG. 8. Significantly higher n-butene conversions occur withmicrocrystalline ZSM-35 with no loss of isobutene selectivity.

EXAMPLE 15

Isomerization of 1-Butene with Large Crystal Synthetic Ferrierite

The synthetic ferrierite of Example 13 was used in 1-butene skeletalisomerization reactions carried out at 400° to 500° C., 66 WHSV, 24psia, using a nitrogen/1-butene feed. The conditions of each run and theproduct composition is set out below in Table 3. At 400° C., conversionwas near zero (0.34%). Conversion did not increase even when temperaturewas raised to 550° C. and WHSV reduced to 33. Conversion did increase to50-60% when WHSV was cut to 2 as depicted in FIG. 9. However,selectivity was low (60-70%) and the catalyst aged rapidly. The rapidaging of the synthetic ferrierite becomes dramatically clear whenn-butene conversion for this catalyst and small crystal ZSM-35 areplotted as a function of cumulative 1-butene throughput as in FIG. 10.Microcrystalline ZSM-35 ages approximately three orders of magnitudemore slowly.

                  TABLE 3                                                         ______________________________________                                        WHSV:        66       33       33     33                                      Temperature (C.):                                                                          400      549      400    299                                     Pressure (PSIA):                                                                           24       30       30     30                                      HOS:         19       23       26     28                                      N2/1-Butene in Feed:                                                                       3        1        1      1                                       ______________________________________                                                     % IN     % IN     % IN   % IN                                    COMPOUND     PROD     PROD     PROD   PROD                                    ______________________________________                                        Methane      0.00     0.00     0.00   0.00                                    Ethane       0.00     0.00     0.00   0.00                                    Ethylene     0.00     0.04     0.00   0.00                                    Propane      0.00     0.00     0.00   0.00                                    Propylene    0.23     0.15     0.05   0.04                                    Isobutane    0.00     0.00     0.00   0.00                                    N-Butane     0.11     0.11     0.07   0.06                                    Trans-2-Butene                                                                             44.53    38.14    45.10  49.94                                   1-Butene     23.14    30.16    22.84  17.66                                   Isobutylene  0.00     0.00     0.00   0.00                                    Cis-2-Butene 31.99    31.31    31.84  32.17                                   Butadiene    0.00     0.00     0.00   0.00                                    3-Methyl-1-Butene                                                                          0.00     0.00     0.00   0.00                                    Trans-2-Pentene                                                                            0.00     0.00     0.00   0.00                                    2-Methyl-2-Butene                                                                          0.00     0.08     0.10   0.04                                    1-Pentene    0.00     0.00     0.00   0.00                                    2-Methyl-1-Butene                                                                          0.00     0.00     0.00   0.00                                    Cis-2-Pentene                                                                              0.00     0.00     0.00   0.00                                    Carbon 6+    0.00     0.00     0.00   0.10                                    Total Pentenes                                                                             0.00     0.08     0.10   0.04                                    TAME Prec. Pentenes                                                                        0.00     0.08     0.10   0.04                                    % Conversion 0.34     0.38     0.22   0.24                                    Sel. for Isobutene (%)                                                                     0.00     0.00     0.00   0.00                                    ______________________________________                                    

EXAMPLE 16

Preparation of Alumina-Bound ZSM-35

A catalyst was prepared by dry mixing the as-synthesized ZSM-35 ofExample 1 with alumina (LaRoche Versal 250) such that the final productcontained 65 parts ZSM-35 and 35 parts alumina. Sufficient water wasadded to obtain a mixture which was extruded to 1/16 inch (1.6 mm)diameter pellets then dried at 100° C. The extrudate was calcined innitrogen at 538° C. for three hours, then exchanged twice with a 1N NH₄NO₃ solution at room temperature, dried at 100° C. and calcined in airfor 6 hours. The product had a pore volume of 0.86 cc/g and a 300⁺angstrom pore volume of 0.46 cc/g.

EXAMPLE 17

Preparation of Large-Pore Silica-Bound ZSM-35

A catalyst was prepared by dry mixing the as-synthesized ZSM-35 ofExample 1 with precipitated silica (Ultrasil™ VNSP3 from Degussa).Colloidal silica, in proportion to give 65% ZSM-35/35% silica aftercalcination, and water were added to the dry mix to obtain an extrudablemixture. The mix was extruded to 1/16 inch (1.6 mm) diameter pellets,and dried at 100° C. The extrudate was calcined in nitrogen at 538° C.for three hours, then exchanged twice with a 1N NH₄ NO₃ solution at roomtemperature, dried at 100° C. and calcined in air for 7 hours. Theproduct had a pore volume of 0.86 cc/g and a 300⁺ angstrom pore volumeof 0.37 cc/g.

EXAMPLE 18

Skeletal Isomerization of 1-Butene with Catalyst Compositions ofExamples 16, 4 and 17

1-Butene was subjected to skeletal isomerization conditions in thepresence of alumina-bound ZSM-35 (Example 16), silica bound ZSM-35 oflower pore volume (Example 4), and silica bound ZSM-35 of enhanced porevolume (Example 17). The conditions comprised 33 1-butene WHSV onzeolite, 1/1 v/v butene/nitrogen feed, 30 psia, and 400° C. usingcatalysts comprising 65 wt% ZSM-35 sized to 14/24 mesh. FIG. 11 comparesthe effects of aging on n-butene conversion for the alumina-boundcatalyst of Example 16, versus the silica-bound catalyst of Example 17,showing a reduction in activity from 46% to 23% n-butene conversion overabout 7 days compared with a reduction in activity from 47% to 30%n-butene conversion over about 18 days, respectively. FIG. 12 comparesthe effects of n-butene conversion on isobutene selectivity for n-buteneconversion for the alumina-bound catalyst of Example 16, versus thesilica-bound catalyst of Example 17. The results show little variationin isobutene selectivity over a range of about 23 to 50% n-buteneconversion between the two catalyst types. FIG. 13 compares the effectsof aging for the silica-bound catalyst of Example 4, versus thesilica-bound catalyst of Example 17, showing a reduction in activityfrom 48% to 28% n-butene conversion over about 12 days compared with areduction in activity from 47% to 30% n-butene conversion over about 18days, respectively. FIG. 14 compares the effects of reduced n-buteneconversion (aging) on isobutene selectivity on n-butene conversion forthe silica-bound catalyst of Example 4, versus the silica-bound catalystof Example 17. The results show little variation in isobuteneselectivity over a range of about 28 to 50% n-butene conversion betweenthe two catalyst types.

While the instant invention has been described by specific examples andembodiments, there is no intent to limit the inventive concept except asset forth in the following claims.

What is claimed is:
 1. A method for conversion of linear olefins tocorresponding iso-olefins of the same carbon number which comprisescontacting a linear olefin-containing organic feedstock comprising C₄ toC₁₀ linear olefins with a catalyst comprising material having thestructure of ZSM-35 under skeletal isomerization conditions, whereinsaid conversion is carried out at temperatures between about 100° and750° C., weight hourly space velocities (WHSV) based on linear olefinsin said feedstock between 0.1 and 500 WHSV, and linear olefin partialpressures between 2 and 2000 kPa, and said catalyst comprises a silicabinder and has a pore volume of greater than 0.66 cc/g or 300⁺ angstromspore volume of greater than 0.1 cc/g.
 2. The method of claim 1 whereinsaid conversion is carried out at temperatures between about 150° and600° C., weight hourly space velocities (WHSV) based on linear olefinsin said feedstock between 0.5 and 400 WHSV, linear olefin partialpressures between 10 and 500 kPa, and conversion levels of at least 20weight percent.
 3. The method of claim 1 wherein said temperatures arebetween about 200° and 550° C., said weight hourly space velocities(WHSV) are between 1 and 100, said linear olefin partial pressure isbetween 20 and 200 kPa, and conversion levels of at least 30 weightpercent.
 4. A method for conversion of linear olefins to correspondingiso-olefins of the same carbon number which comprises contacting underskeletal isomerization conditions a linear olefin-containing organicfeedstock comprising C₄ to C₁₀ linear olefins with a catalyst comprisinga) material having the structure of ZSM-35 having a crystal size whoselargest dimension is no greater than 0.5 micron, and whose ratio of itssecond largest dimension to said largest dimension ranges from 0.5 to1.0, and b) a silica binder.
 5. The method of claim 4 wherein saidconversion is carried out at temperatures between about 100 and 750° C.,weight hourly space velocities (WHSV) based on linear olefins in saidfeedstock between 0.1 and 500 WHSV, and linear olefin partial pressuresbetween 2 and 2000 kPa, and wherein said ZSM-35 has a crystal size whoselargest dimension is no greater than 0.25 micron.
 6. The method of claim4 wherein said conversion is at least 20 weight percent.
 7. The methodof claim 4 wherein said temperatures are no greater than 450° C.
 8. Themethod of claim 4 wherein said WHSV is no less than
 1. 9. The method ofclaim 4 wherein said largest dimension of said crystal size is nogreater than 0.1 micron.
 10. The method of claim 4 wherein said crystalsize has the dimensions of 0.03 to 0.08 micron by 0.03 to 0.08 micron by<0.05 micron.
 11. The method of claim 4 wherein said catalyst has atotal pore volume greater than 0.6 cc/g or 300⁺ angstroms pore volume ofgreater than 0.1 cc/g.
 12. The method of claim 4 wherein said organicfeedstock comprises at least 5 wt % n-butenes.
 13. The method of claim 4wherein said feedstock comprises C₄ to C₆ linear olefins.
 14. The methodof claim 4 wherein said organic feedstock consists essentially of a C₄hydrocarbon stream.
 15. The method of claim 4 wherein said organicfeedstock consists essentially of a C₄₊ hydrocarbon stream.
 16. Themethod of claim 4 wherein said organic feedstock comprises at least 5 wt% n-pentenes.